Model-based estimation of the canopy transpiration of Qinghai spruce (Picea crassifolia) forest in the Qilian Mountains Characteristic of Picea crassifolia forest soil organic carbon and relationship with environment factors in the Qilian Mountain Effects of Temperature on Soil Respiration in Picea crassifolia Forest of Qilian Mountains Altitudinal Changes in Structure of Middle-aged Picea crassifolia Forests on the Northern Slope of the Qilian Mountains